A list of errata was provided with my copy of the book. The corrections have been made in the midi files and are indicated with the chants concerned; a few additional (print) errors have also been corrected

Note: Obligato organ part (left out in the midi, included in 286-2)
print error: tenor bar 12 F minim should read F natural minim (this note is not tied, as in the organ part, so the natural is necessary)